A diesel engine may be supplied with different types of diesel fuel that range from low cetane number diesel fuel to high cetane number diesel fuel. Higher cetane number diesel fuels exhibit shorter ignition delays (e.g., an amount of time between start of injecting fuel to a cylinder during a cycle of the cylinder to a pressure increase due to onset of combustion of the injected fuel) while lower cetane number diesel fuels exhibit longer ignition delays. If an engine is started with lower cetane number diesel fuels at colder engine temperatures, it may take longer to heat a catalyst coupled to the engine because of combustion stability limits. Further, hydrocarbon emissions may degrade at lower engine temperatures if lower cetane fuel is supplied to the engine. On the other hand, the engine may perform well after it is warm and combusting the lower cetane fuel. Therefore, it may be desirable to provide a way of improving engine cold starting after a vehicle's fuel tank is filled with lower cetane fuel.
The inventor herein has recognized the above-mentioned disadvantages and has developed an engine method, comprising: mixing a cetane enhancing fluid with diesel fuel having a first cetane number to provide diesel fuel having a second cetane number; pumping the diesel fuel having the second cetane number to a high pressure fuel pump via a low pressure fuel pump; and injecting the diesel fuel having the second cetane number to an engine in response to starting the engine when a catalyst temperature is less than a threshold.
By mixing a cetane enhancing fluid with diesel fuel, pumping the mixture to a high pressure pump, and injecting the fuel mixture to an engine in response to starting an engine and catalyst temperature being less than a threshold, it may be possible to reduce engine emissions and improve catalyst light off time after an engine start. In particular, fuel injection timing may be retarded when cetane enhanced diesel fuel is injected to an engine after an engine start since combustion stability may be improved. The retarded fuel injection timing may reduce catalyst light off time and higher cetane fuel may reduce hydrocarbon emissions while fuel injection timing is retarded from nominal fuel injection timing (e.g., fuel injection timing at a present engine speed and engine output torque during warm engine operating conditions).
The present description may provide several advantages. Specifically, the approach may reduce engine emissions. In addition, the approach may improve engine combustion stability during cold engine operating conditions. Further, the approach may provide enhanced engine starting characteristics for engines that have a single fuel injector for each engine cylinder.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.